The present invention relates to an ink supply device for supplying an ink for an ink-jet type image formation apparatus, and a method for filling the ink.
Ink-jet type image formation apparatuses have been widely used for formation of an image on a recording medium. The ink-jet type image formation apparatus, for example, has a printing head having a nozzle for ejecting an ink, and a carriage reciprocating in a prescribed direction with the printing head held thereon. The maximum amount of the ink stored in the printing head is limited to avoid an excessive weight of the reciprocating carriage.
To solve this problem, ink supply device 10 as shown in FIG. 17 is used in which ink tank 12 of a large capacity is placed separately from the carriage (not shown in the drawing), and from this ink tank 12 an ink is supplied through ink supply tube 14 to printing head 16. Printing head 16 has ink pool 20 therein for storing liquid ink (raw ink) 18. This ink 18 stored in ink pool 20 is ejected from nozzle 22. Ink pool 20 of printing head 16 may be constructed from a hard wall, or a soft bag expandable by a plate spring from the periphery.
In the ink pool constructed of a hard wall, the volume of air in ink pool 20 changes with the use of the ink. The volume of the air changes also depending on the environmental temperature. As the results, the pressure exerting on the ink stored in ink pool 20 varies to vary the amount of the ink to be fed to nozzle 22. Therefore, the variation of the use of the ink and the environmental temperature will cause variation of the amount of ink ejection through nozzle 22, which can deteriorate the image quality. Further, since printing head 16 moves with the carriage, the ink in ink supply tube 14 is moved by inertial force to vary the amount of the ink stored in ink pool 20 to vary the air volume in ink pool 20. In this case also, the image quality can be deteriorated by variation of the amount of ejection of the ink.
On the other hand, in ink pool 20 constructed from a soft bag expandable by a plate spring, the amount of the air in the tank is controlled by the plate spring to decrease the variation thereof to stabilize relatively the amount of the ink ejected from nozzle 22. However, the use of the plate spring and the soft bag complicates the structure of ink tank, disadvantageously.
In the both cases of the solid wall-surrounded ink pool and the soft bag type ink pool an impurity may contaminate the ink in operation of connection or disconnection of ink supply tube 14, or exchange of ink tank 12. The impurity contaminating the ink can reach nozzle 22 to clog nozzle 22, disadvantageously.
Furthermore, the liquid surface level of the ink stored in ink tank 12 goes down with consumption of the ink, so that the vertical distance between the liquid surface level and nozzle 22 becomes larger with consumption of the ink, causing variation of the amount of the ink ejected through nozzle 22 to deteriorate the image quality. This ink level lowering can be prevented by making ink tank 12 flat to decrease the depth of the ink, but it requires a larger space therefor. Otherwise, a float or a valve may be provided in ink tank 12, or a negative pressure-generating mechanism may be provided in the printing head to decrease the variation of the amount of the ink ejected through nozzle 22. With any of the above techniques, the construction becomes complicated, disadvantageously.
For filling the ink for the first time from ink tank 12 into ink supply tube 14, the ink is usually sucked by a head-recovering suction pump for the printing head recovery, or sucked by a negative pressure generated by connection of a negative pressure-generating means such as a syringe to the outlet of ink supply tube 14.
The negative pressure generated by the head-recovering suction pump is not sufficient, so that the suction operation should be repeated several times for filling the ink into ink supply tube 14, which takes a long time. When the negative pressure-generating means is used for filling the ink into ink supply tube 14, the operation is not simple, and may cause soiling of hands and other disadvantages.
The present invention intends, under the above circumstances, firstly to provide an ink supply device which is capable of supplying the ink in an stable amount to eject through the nozzle. The present invention intends secondly to provide an ink filling method for filling smoothly an ink into an ink supply tube.
In an ink-jet type image formation apparatus having a carriage reciprocating in a prescribed direction and forming an image by ejection of ink on a recording medium, the ink supply device of the present invention for achieving the above first object comprises a printing head having a nozzle and being mounted on the carriage, an ink tank for storing the ink to be supplied to the printing head, and an ink supply tube for supplying ink from the ink tank to the printing head, wherein
(1) the printing head has a built-in porous mass of an open-cell structure communicating with the nozzle, and
(2) the ink supply tube is connected at the one end to the porous mass, and the ink tank, the ink supply tube, and the printing head are connected hermetically.
The porous mass of an open-cell structure means the one which has holes communicating with each other.
The ink supply device may have
(3) an ink supply pipe which is connected to the one end of the ink supply tube and is inserted into the porous mass.
(4) The tip of the ink supply pipe may be inserted into the center portion of the porous mass or into the portion thereof nearer to the nozzle than the center portion.
(5) The ink supply pipe may have an ink supplying through-hole on the side wall thereof.
(6) The porous mass may be the one which is capable of absorbing the pressure variation in the ink supply tube by capillarity.
The ink tank may comprise
(7) an open tank which contains the ink with the surface of the ink open to the atmospheric air, and
(8) additionally a closed ink tank which is placed above the open ink tank, storing the ink in a closed state, and having a connection pipe extending vertically to come into contact with the ink in the open tank.
The open ink tank
(9) may be placed such that the surface level of the stored ink is lower than the position of the nozzle of the printing
The ink supply device
(10) may have a joint member which is attached to the tip end of the ink supply tube and connects the ink supply tube detachably and hermetically to the printing head.
The ink supply device
(11) may have a joint housing room formed in the carriage for housing the joint member.
The joint housing room
(12) may be provided in the same number as the number of the joint members connected to the printing head mounted on the carriage.
The ink supply device
(13) may have a cover for covering the joint housing room.
The joint member may have
(14) a first connection orifice for connection with the tip portion of the ink supply tube,
(15) a second connection orifice for connection of the ink supply pipe,
(16) a third connection orifice separated from the first and second openings, and further
(17) a sucking device connected to the third connection orifice to suck the ink.
The sucking device may have
(18) an ink-filling adapter to be inserted into the third connection orifice to communicate with the first connection orifice and not to communicate with the second connection orifice.
(19) The third connection orifice may have a groove extending in the direction of insertion of the ink-filling adapter on the inside wall thereof, and
(20) the ink-filling adapter may have, on the outer face thereof, a rib to fit to the groove.
The ink filling method of the present invention for achieving the above second object comprises ink filling steps:
(21) connecting a sucking device for sucking of the ink with the third connection orifice, closing the second joint opening of the joint member, and
(22) sucking the ink with the sucking device to fill the ink into the ink supply tube.